Yaffe Omer, Guo Yinsheng, Tan Liang Z, Egger David A, Hull Trevor, Stoumpos Constantinos C, Zheng Fan, Heinz Tony F, Kronik Leeor, Kanatzidis Mercouri G, Owen Jonathan S, Rappe Andrew M, Pimenta Marcos A, Brus Louis E
Department of Chemistry, Columbia University, New York, New York 10027, USA.
Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Phys Rev Lett. 2017 Mar 31;118(13):136001. doi: 10.1103/PhysRevLett.118.136001. Epub 2017 Mar 28.
Hybrid lead-halide perovskites have emerged as an excellent class of photovoltaic materials. Recent reports suggest that the organic molecular cation is responsible for local polar fluctuations that inhibit carrier recombination. We combine low-frequency Raman scattering with first-principles molecular dynamics (MD) to study the fundamental nature of these local polar fluctuations. Our observations of a strong central peak in the cubic phase of both hybrid (CH_{3}NH_{3}PbBr_{3}) and all-inorganic (CsPbBr_{3}) lead-halide perovskites show that anharmonic, local polar fluctuations are intrinsic to the general lead-halide perovskite structure, and not unique to the dipolar organic cation. MD simulations indicate that head-to-head Cs motion coupled to Br face expansion, occurring on a few hundred femtosecond time scale, drives the local polar fluctuations in CsPbBr_{3}.
混合卤化铅钙钛矿已成为一类出色的光伏材料。最近的报告表明，有机分子阳离子是抑制载流子复合的局部极性波动的原因。我们将低频拉曼散射与第一性原理分子动力学（MD）相结合，以研究这些局部极性波动的基本性质。我们对混合（CH₃NH₃PbBr₃）和全无机（CsPbBr₃）卤化铅钙钛矿立方相中的强中心峰的观察表明，非谐性局部极性波动是一般卤化铅钙钛矿结构所固有的，并非偶极有机阳离子所特有。MD模拟表明，在几百飞秒时间尺度上发生的与Br面扩展耦合的Cs头对头运动驱动了CsPbBr₃中的局部极性波动。
